Control arrangement for discharge devices



Sept. 30, 1947. BRAKEL fi 2,428,008

CONTROL ARRANGEMENT FOR DISCHARGE DEVICES I Filed March 1, 1944INVENTQRSZ LESLIE BRAKEL,

R0 ERT T. THOMPSON BYS THEIR ATTORNEY Patented Sept. 30, 1947 CONTROLARRANGEMENT FOR DISCHARGE DEVICES Leslie Brakel, Eugene, Greg, andRobert T. Thompson, Oak Park, 111., assignors to Zenith a corporation ofIllinois Application March 1, 1944, Serial No. 524,556

Radio Corporation,

6 Claims.

This invention relates to control apparatus for an electron dischargedevice having a cathode which assumes its normal operating temperature arelatively long time after it is heated initially.

In radio receivers and transmitters wherein the electron dischargedevices have indirectly heated cathodes, a relatively long period oftime is required to bring such cathodes up to correct operatingtemperature after the receiver or transmitter is energized with currentfrom an operating source. It is desirable to make such period of time asshort as possible'so that an operator need not wait a relatively longperiod of time after closing the power switch before he is able to tuneor adjust the radio apparatus.

It is not an uncommon occurrence for people to close the power switch ofa radio receiver, then walk away from the receiver and then later hearloud and objectionable sounds or blasts emanating from the receiver assoon as the cathodes in the discharge devices in the receiver have beenheated to their normal operating temperatures. Such occurrences are notonly objectionable to people in the near vicinity but also detract muchfrom the listening 'pleasureof the operator. In those instances wherethe operator is cautious, he must wait a relatively long period of timeat the receiver and attentively wait for the cathodes of the dischargedevices to come up to substantially normal operating temperature beforehe leaves the vicinity of the receiver. This, of course, not onlyconsumes some time but also requires some attention, however slight, bythe operator, and in some cases is the determining factor whether thereceiver is turned on or left inoperative. It is therefore an object ofthis invention to provide improved apparatus for causing radio apparatusto be operative for normal reception or transmission of signals within anegligible time after the power switch to the radio apparatus is closed,such time interval'preferably being in the order of two or threeseconds.

Moreover, when the power switch of a conventional radio receiver ortransmitter supplied with power from an alternating current source isclosed, relatively large surge voltages, dying down to somewhat smallersteady stage voltages, exist across condensers in the rectifying circuitand receiving circuit proper until the cathodes of the discharge tubescome up to normal operating temperature, in which case the resultingconductivity of the discharge devices causes a current flow andconsequent lowering of the voltages throughout the rectifying circuitand receiving circuit proper. Since such condensers must not onlywithstand normal operating voltage stresses but also these transientvoltage stresses when the power switch is moved from its 0 position toits on position, such condensers are in some instances relatively largeand relatively expensive. Another object of the present invention is toprovide improved control apparatus for circuits including dischargedevices such that circuit elements in such circuits are not subjected tounduly large transient stresses when the circuit is connected to a powersupply for signal reception.

When a receiving or transmitting circuit having electron dischargedevices of the heater cathode type is connected toits power supply, thecathodes and their heaters not only become hot but also expand due totheir coeflicients of expansion, and, of course, contract when the powersupply is disconnected. Switching on and ofif such a receiving ortransmitting circuit not only changes the electron emission of thecathode but also causes motion of the cathode and its related parts.When the cathode and its heater are not subjected to such largetemperature gradients their relative movements are reduced and theoverall life of the cathode is increased. Another object of the,present'invention is to provide a control arrangement for circuitsincluding elec tron discharge devices of the heated cathode type inwhich the cathode and its heater are not subjected to large differencesin temperature when the circuit is changed from its operative conditionto its inoperative condition.

Also, in a receiver or transmitter wherein good frequency stability isdesired after'the receiver or transmitter is connected to an operatingsource of potential, it is desirable that the cathodes of dischargedevices in such receiver or transmitter be preheated so that'changes inoperating frequency are minimized.

Still another objectof this invention is to provide an improved controlarrangement for receiving or transmitting circuits having an offposition, a standby position and an on position.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. This inventionitself, both as to its organization and manner of operation, togetherwithlfurther objects and advantages thereof, may best be understood byreference to the following description taken in connection with theaccompanying drawing in which the single figure'shows a radio receivingcircuit controlled in accordance with the present invention.

The present invention relates to a circuit including electron dischargedevices having heated cathodes, such as indirectly heated cathodes orfilamentary cathodes, and for purposes of illustration the invention isshown in relation to a radio receiver of the amplitude modulation type,it being understood, however, that this invention may be used in othercircuits with an electron discharge device having a heated cathode; forexample, th present invention may be applied to transmitter circuits,cathode ray tube circuits, thyratron tube circuits, et cetera. By theterm heated cathodes throughout this specification it is realized thatsuch term includes indirectly heated cathodes and filamentary types ofcathodes which have heating current passing therethrough.

The figure shows an arrangement for heating the cathodes of dischargedevices in a pushbutton tuned radio receiver which may be operative forsuitable reception of high frequency signals received on antenna 9 ashort time after the heaters for such cathodes are energized with normalcurrent.

In the figure is shown a radio receiver of the superheterodyne typeincluding, in cascade, a radio frequency amplifying stage ID, apentagrid converter or oscillator-modulator stage II, an intermediatefrequency amplifying stage l2, a detecting stage l3, an audio amplifyingstage l4, and an audio power amplifying stage l5. Each of such stagesincludes electron discharge devices having cathodes of the indirectlyheated type and being supplied with space current from a common voltagesource 8. It is understood that the cathode of such devices may be ofthe indirectly heated cathode type or of the directly heated heavyfilamentary cathode type which heats up slowly to suitable electronemission temperature after normal voltage is applied to the terminals ofsuch heaters or cathodes.

The present invention relates particularly to circuit arrangements forheating the cathodes of those devices such that the cathodes emitsufficient electrons within a very short time, such as two or threeseconds, after it is desired to change the radio receiver frominoperative condition to a condition operative for satisfactoryreception of signals.

The figure shows a receiver arranged to receive modulated waves onantenna 9 and to reproduce signals corresponding to such modulation inreproducer or speaker I. The receiver is of the pushbutton tunedsuperheterodyne type, including variably tuned circuits in a radiofrequency amplifying stage, and in the frequency converter oroscillator-modulator stage I l. The tuned circuits, tuned atpredetermined frequencies, are inserted by actuating one of a series ofpushbuttons 24 in conventional manner.

The fixed frequency output of the oscillatormodulator or frequencyconverter stage I I is amplified through a fixed frequency intermediatefrequency amplifier l2, and the modulating components of the signal aredetected in detector [3, and such modulating components separated fromthe carrier wave, are amplified in the audio amplifyingstage I4 and I5and then applied to speaker I, so that speaker I reproduces thosemodulating components of a broadcast frequency to which the receiver istuned by connecting suitable reactances in the stages In and II by meansof one of a series of pushbuttons 24 in conventional manner.

The series of pushbuttons 24 is, in conventional manner, latchedtogether by means of a common latch bar 25 so that only one of thepushbuttons 24 is in operative position at any one time. In accordancewith the present invention, latch bar 25 serves also to hold in latchedposition one of a series on, ofi and standby pushbutton switches 30, 3|and 32, respectively, in a manner shown in the drawing and more fullydescribed in the copending application Of Robert T. Thompson, Serial No,524,555, filed on even date herewith and assigned to the same assignee.Also, as shown herein and in the copending application, link member 26extends from the series of pushbuttons 24 to the on pushbutton 32 sothat the composite radio receiver is made fully operative when any oneof the series of tuning pushbuttons 24 is depressed.

The voltage source for supplying space current to the discharge devicesin the receiver comprises alternating current rectifying apparatushaving the general reference numeral 8. The positive terminal of suchapparatus is connected to lead 34 of positive continuous voltage throughwhich the entire space current flows.

In the'figure, the heaters l6, l1, I8, I9, 20 and 2| are each connectedin parallel circuit relationship with one another so that the voltageexisting. across the terminals of one of the heaters is substantiallythe same voltage existing across each of the terminals of the otherheaters. For that purpose, one terminal of each of the heaters isconnected to a common conductor 22 and the other terminal of each of theheaters is connected to another common conductor 23.

The apparatus to be described now allows three alternating voltages ofdifferent magnitudes to be impressed between the conductors 22 and 23,namely, zero voltage, a normal operating voltage and a relatively smallvoltage in standby operation of the receiver.

Heating current for the parallel connected heaters is supplied fromlines 35 and 36, carrying, for example, normal household alternatingpotential through transformers 31 and 38 when the receiver is fullyoperative and through transformer 31 alone when the receiver isconditioned for standby operation.

The primary winding 39 of transformer 38 has one of its terminalsconnected to line 35 and its other terminal connected to line 35 throughon" pushbutton switch 32 having a pair of normally open contacts 43 and44, lead 46 of winding 39 being connected to one of the terminals ofnormally open switch 44 and the other terminal of switch 44 beingconnected to lead 35.

The primary winding 50 of transformer 31 has one of its terminalsconnected to line 35 and its other terminal connected to line 35 eitherthrough the standby switch 3| or through the 011" switch 32, as the casemay be. In particular, lead 52 of winding 50 is connected to one of theterminals of normally open switch 3| and to one of the normally opencontacts of switch 43 on on" switch 32, the other terminals of switches3| and 43 each being connected to lead 35 so that the voltage appearingacross leads 35 and 36 is applied across primary winding 50 when eitherswitch 3| or switch 32 is actuated. Also, when switch 32 is actuated,the voltage appearing across leads 35 and 36 is applied across theprimary winding 39 of transformer 38.

As explained previously, pushbutton switches 30, 3| and 32 are latchedto the series of tuning pushbuttons 24 through latch member 25 so thatonly one of the pushbutton switches including tuning pushbuttons 24 isheld in depressed position at one particular time, with the exceptionthat, due to link member 26, on pushbutton 32 may be held in depressedposition together with one of the tuning pushbuttons 24.

The secondary winding 55 of transformer 33 is connected in seriescircuit relationship with secondary winding 56 of transformer 31, theunconnected terminal of winding 55 being connected to common conductor23and the unconnected terminal of winding 56 being connected to the othercommon conductor 22.

When the on pushbutton 32 is depressed, the total voltage induced insecondary windings 55 and 56, connected in series aiding relationship,is applied between the common conductors 22 and 23 and full normaloperating voltage for suitable operation of the receiving circuit existsacross each one of the heaters |6,"|"|, |8, I9, 20 and 2|.

When the standby pushbutton 3| is depressed, the primary winding 50 onlyis connected to lines 35 and 36 and the voltage induced in secondarywinding 56 alone is applied to leads 22 and 23, the secondary winding 55in such case constituting a current path for flow of reduced heatercurrent to heaters l6, I1, I8, I9, 20 and 2|, a study of the figurereveals that secondary winding 55 must be so wound as to have, whenprimary 39 is open circuited, a leakage reactance which is smallcompared to the resistance presented by heaters l6, |1, l8, I9, 20, and2|, in parallel, while at the same time it must provide, when primarywinding 39 is energized, sufiicient voltage to bring up the heatervoltage from the stand-by to the full operating value.

When off pushbutton 30 is depressed, of course, the pushbuttons 3| and32 are released and neither transformer 31 nor transformer 38 isenergized and consequently no heater voltage exists between leads 22 and23,

A suitable continuous potential for the anodes and screen grids of thedischarge devices in the radio receiver exists on lead 34 only whenpushbutton 32 is depressed, in which position full normal heater voltageexists between conductors 22 and 23. Such continuous potential isdeveloped by rectifying and filtering the alternating potential existingacross leads 35 and 36 in a manner described now.

Alternating current voltage induced in center tapped secondary winding60 of transformer 38 when pushbutton 32 is depressed is applied betweenthe anodes 6| and 62 of a full wave rectifying device 64, one of theterminals of winding 60 being connected to anode 6|, the other terminalof winding 60 being connected to anode 62 and the center tap beinggrounded. The filament type cathode of device 64 is heated byalternating current flowing from center tapped secondary winding 65 oftransformer 33 through such cathode when switch 33 is in its onposition, the ends of winding 65 being connected to opposite terminalsof the cathode and the center tap being connected to lead 34 through aconventional filter circuit comprising serially connected filterinductance 66 having one of its terminals grounded through filtercondenser 67 and its other terminal grounded through filter condenser68.

With this arrangement in the figure, lead 34 is of suitable positivepotential with respect to ground when pushbutton 32 is depressed and thereceiver is operative to reproduce the modulated components of thesignal waves impressed on antenna 9.

When standby switch 3| is depressed, the poheaters l5, l1, l8,

tential of lead 34 is substantially zero with respect to ground andreduced heating current flows through the cathode heaters of thedischarge devices in the receiver.

The amount of current which fiows through i9, 20 and 2| when standbypushbutton 3| is depressed is such as to cause the receiver to becomefully operative in two or three seconds after pushbutton 32 is depressedto release pushbutton 3|, it being understood that the cathode ofrectifying device 64 is of the filament type and that it comes up tocorrect operating temperature within such time interval of two or threeseconds.

In the figure, when pushbutton 30 is depressed, no heating current flowsand the potential of lead 34 is zero.

The arrangement shown in the figure is characterized by the fact thatthe receiver consumes a relatively small amount of power when pushbutton3| is depressed, thus allowing a user to maintain his receiver in thatcondition throughout the day without appreciable power consumption inwhich condition it is effective to preheat the cathodes 16, 11, I8, 19,and 8| such that the receiver is fully operative for suitable receptionof broadcast signals two or three seconds after on pushbutton 32 isdepressed to release standby pushbutton 3|.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without depart.- ing from thisinvention in its broader aspects, and therefore the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of this invention.

We claim:

1. In combination, a discharge device having a cathode, a heater for thecathode, a first transformer having a primary winding arranged to beenergized from a source of alternating potential and having a secondarywinding, a second transformer magnetically independent of said firsttransformer having a primary winding arranged to be energized from asource of alternating potential and having a secondary winding, saidheater together with said secondary winding of the first mentionedtransformer and said secondary winding of the second mentionedtransformer being serially connected, means for selectively energizingonly one of said primary windings, and means for energizing the primarywindings of both transformer simultaneously,

2. In combination, a discharge device having a cathode, an anode and aheater, a rectifying device, a first transformer having a high voltagesecondary winding connected to the rectifying device when supplyingspace current between the cathode and anode, a second secondary windingon the first transformer connected to the heater for supplying a currentto the heater, a second transformer magnetically independent of saidfirst transformer having its secondary winding connected to supply anadditional current to said heater, means for selectively energizing onlyone of said transformers through its primary winding, and means forenergizing said transformers simultaneously through their primarywindings.

3. In combination, an electron discharge device including anelectrically heated electron source having a pair of filament terminalsfor the flow of heating current, a pair of magnetically independenttransformers each having a primary and secondary winding, a source ofalternating potential, said terminals and said two secondary windingsbeing connected serially, means for el tively energizing only one ofsaid primary windings from said potential source, and means forenergizing the primary windings of both transformers simultaneously fromsaid potential source.

4. In combination, an electron discharge device including a cathode, aheater for said cathode, a pair of magnetically independent transformersat least one of which has a primary and a secondary winding and bothtransformers having input and output terminals, the respective outputterminals of each transformer having an output winding therebetween andat least one of said output windings being said secondary winding, asource of alternating potential said heater and said output windings allbeing connected serially, means for selectively energizing only one ofsaid transformers from said potential source and means for energizingboth of said transformers simultaneously from said potential source.

5. In combination, an electron discharge device including anelectrically heated electron source having a pair of filament terminalsfor the flow of heating current, a pair of magnetically independenttransformers at least one of which has alprimary and a secondary windingand each of which has input and output terminals, the respective outputterminals of each transformer having an output winding therebetween, andat least one of said output windings being said secondary winding, asource of alternating potential, said output windings and said filamentterminals being connected serially, means for selectively energizing oneof said transformers from said potential source, and means forenergizing both of said transformers simultaneously from said potentialsource.

'6. In combination, an electron discharge device including anelectrically heated electron source having a pair of filament terminalsfor the flow of heating current, and an anode, a first trans formerincluding a primary winding, a high voltage secondary winding and a lowvoltage secondary winding, a rectifier device connected to said highvoltage secondary winding, said rectifier device being connected tosupply operating potential between said anode and said electron source,said low voltage secondary winding being connected to said filamentterminals to supply heating current to said electron source, a secondtransformer magnetically independent of said first transformer having aprimary and a secondary winding, said secondary winding being connectedto supply heating current to said electron source in addition to thatsupplied by said low voltage secondary winding .of said firsttransformer, a source of alternating potential,.rneans for energizingonly the primary winding of said second transformer from said potentialsource, and means for energizing the primary windings of bothtransformers simultaneously from said potential source.

LESLIE BRAKEL.

ROBERT T. THOMPSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,896,768 Chubb Feb. '7, 19332,290,819 Warshawsky July 21, 1942 1,904,839 Stenzy Apr. 18, 1933FOREIGN PATENTS Number Country Date 371,578 Great Britain Apr. 28, 193212,391 /28 Australia Mar. 20, 1928

